BUG #16511: Using '= all ( )' with empty table returns true
The following bug has been logged on the website:
Bug reference: 16511
Logged by: Anton Luhavy
Email address: anton.lugovoy.hopni@gmail.com
PostgreSQL version: 10.7
Operating system: MacOS
Description:
Given table is "task" (id uuid primary key, status text not null),
Query "select 'b' = all (select status from task where status = 'a')"
returns true if table "task" is empty
PG Bug reporting form <noreply@postgresql.org> writes:
Given table is "task" (id uuid primary key, status text not null),
Query "select 'b' = all (select status from task where status = 'a')"
returns true if table "task" is empty
Why do you think that's wrong? It matches usual mathematical practice,
and even if you dispute that, the SQL standard is quite explicit about it:
1) Let R be the result of the <row value constructor> and let T be
the result of the <table subquery>.
...
a) If T is empty or if the implied <comparison predicate> is
true for every row RT in T, then "R <comp op> <all> T" is
true.
regards, tom lane